Approximately 500 children are diagnosed with AML every year, of whom around 60% are cured with current regimens based on anthracyclines and high dose cytarabine with or without stem cell transplant (SCT). Among the remaining 40% who are refractory or who relapse, outcome is dismal. Additionally, 20-30% of patients with childhood ALL relapse or become refractory to frontline therapies. The prognosis is poor in this patient population, particularly in patients with second or subsequent relapse and those who relapse following SCT. These patients present myriad challenges, as they usually have received a high cumulative anthracycline dose, and in the case of SCT, may have had significant organ toxicities and/or total body irradiation (TBI). Therefore, new therapeutic strategies need to be identified to enhance possible improved outcomes.